Heretofore, there has been generally known a pressuresensitive copying paper utilizing a color developing reaction between a substantially colorless chromogenic substance and an adsorptive or reactive compound (hereinafter referred to as a developer) which develops a color when it contacts the chromogenic substance. See, for example, U.S. Pat. Nos. 2,505,470; 2,505,471; 2,505,489; 2,548,366; 2,712,507; 2,730,456; 2,730,457 and 3,418,250. Examples of the chromogenic substances are Malachite Green Lactone, Benzoyl Leuco Methylene Blue, Crystal Violet Lactone, Rhodamine B Lactam, 2-(substituted amino)-6-(substituted amino) fluoran, 3-methyl-2,2-spiro- (benzo[f]chromene) and a mixture thereof. Examples of the developers are clay minerals such as acid clay, activated clay, attapulgite, zeolite, bentonite and kaolin; organic acids such as succinic acid, tannic acid, gallic acid and phenolic compounds; and acidic polymers such as a phenol- formaldehyde resin. The chromogenic substance and the developer employed herein are defined as follows from the viewpoint of electronic theory: the chromogenic substance means a substance which develops a color by donating electrons or by accepting protons, and the developer means a substance which accepts electrons or donates protons.
The requirements for the chromogenic substance used in the record material are that it has a high speed of color development, that it has a high color density, that the color-developed chromogenic substance has a desired hue, that it has no sublimability and that the light fastness and heat resistance of the color-developed chromogenic substance are excellent. However, though Crystal Violet Lactone is known as the chromogenic substance developing a blue color, the developed color has poor light fastness. It has thus been desired to develop a chromogenic substance which can satisfy the above-described requirements.
On the other hand, 2-chloro-3-methyl-6-diethylaminofluoran represented by the following formula (A) (hereinafter referred to as compound A) is used as a chromogenic substance which develops a vermilion color though it is inferior in sublimation resistance. See Japanese Examined Patent Publication No. 4701/1970. ##STR2##